Impact type seismic generators have been manufactured for a number of years and successfully used for imparting seismic signals into the earth. Most such apparatus have been designed for use in an air environment. Examples of such apparatus are shown in U.S. Pat. No. 4,660,674, issued Apr. 28, 1987 to Tom P. Airhart; U.S. Pat. No. 4,402,381, issued Sept. 6, 1983 to Tom P. Airhart; U.S. Pat. No. 4,721,181, issued Jan. 26, 1988 to Tom P. Airhart et al.; and U.S. Pat. No. 4,702,344, issued Oct. 27, 1987 to Tom P. Airhart. In each of the foregoing, the impact mass travels through whatever environment the seismic generating apparatus is located.
U.S. Pat. No. 4,284,164, issued Aug. 18, 1981 to Tom P. Airhart and U.S. Pat. No. 4,284,165, issued Aug. 18, 1981 to Tom P. Airhart et al. each disclosed impact type seismic generating apparatus wherein a housing extends around the impact mass which is located in the generating apparatus, to a base plate or coupling that is utilized to transfer the impact force into the soil. In such apparatus, perforations are provided that extend through the housing and thus, if the generator were used in an underwater environment, the housing would fill with water. The water would impede the movement of the impact mass toward its engagement with the base plate. It will be further noted, that such apparatus cannot be positioned at an angle. Thus, and even if the perforations were eliminated, the apparatus would be capable of generating only compressional seismic waves.
U.S. Pat. No. 4,799,572, issued Jan. 24, 1989 to Tom P. Airhart describes an amphibious seismic source wherein the generator, lifting mechanism and all associated parts are contained within a flexible housing that is connected to the periphery of the base plate. The housing prevents water from impeding the impact mass during the generation of seismic signals.
An object of this invention is to provide apparatus for imparting seismic signals into the earth of the impact type that includes a housing encompassing a portion of the seismic generator and extending toward the coupling. Gas pressure within the housing evicts waters therefrom and prevents the entrance of water into the apparatus when used in an underwater environment. The housing aids in confining noise produced by the apparatus when used in an atmospheric environment.